1. Field of the Invention
The invention relates to polycarbonate resins and more particularly to thermoplastic, aromatic polycarbonate resins useful for molding articles which are stable under relatively high temperature conditions.
2. Brief Description of Related Art
Phenolphthalein, as a dihydric phenol reactant, has been used to prepare polycarbonate resins; see for example the disclosures in U.S. Pat. Nos. 3,036,036; 3,036,037; 3,036,039; 4,078,999; 4,167,536; and 4,310,652. Phenolphthalein has also been used as a reactant in admixture with bisphenol-A to prepare copolycarbonate resins; see for example Lin, M.S. and E.M. Pearce, Polymers With Improved Flammability Characteristics, II: Phenolphthalein Related Copolycarbonates, Journal of Polymer Science: Polymer Chemistry Edition, (1981) 19: p.2151-2160. Poly(ester-carbonates) prepared with phenolphthalein reactant are also known; see U.S. Pat. No. 4,310,652.
The phenolphthalein copolycarbonates exhibit excellent ductility and high heat-distortion temperatures. However, the presence of even small quantities of phenolphthalein residues in the product resins, or in the brine medium used in preparation affords discolored resin and recycle water (pink coloration). This is not desirable for many commercial purposes. It has also been reported (Lin, M.S. and E.M. Pearce, Polymers With Improved Flammability Characteristics. I. Phenolphthalein Related Homopolymers. Journal of Polymer Science: Polymer Chemistry Edition, (1981) 19: p.2659-2670) that phenolphthalein based polycarbonate resins are difficult to melt process because of cross-linking and chain scission through the lactone ring; see also Lin, M.S., B.J. Bulkin, and E.M. Pearce, Thermal Degradation Study of Phenolphthalein Polycarbonates, Journal of Polymer Science: Polymer Chemistry Edition, (1981) 19: p.2773-2797 at page 2774.
Certain derivatives of phenolphthalein have also been used as dihydric phenols to prepare polycarbonate resins. For example, Lin and Pearce, I: Pgs. 2151-2160, supra., describe preparation of polycarbonate homopolymer resins wherein 3,3-bis(p-hydroxyphenyl)phthalimidine and 2-phenyl-3,3-bis(p-hydroxyphenyl) phthalimidine were separately polymerized (phosgenated).
We have found the copolymerization of 3,3-bis(p-hydroxyphenyl)phthalimide with bisphenol-A polycarbonate to be extremely difficult because of what appears to be concurrent side reactions through the amide hydrogen during polymerization. These side reactions cause emulsification during interfacial polymerizations, which hinders pH control, molecular weight control and work up of the polymer.
Copolymers of 2-phenyl-3,3-bis(p-hydroxyphenyl)phthalimide were found to have poor melt stability during melt processing resulting in foamy polymer melts and moldings, and discoloration of the resin during melt processing.
Aromatic polyesters of phenolphthalein were found to have better UV stability than both the bisphenol-A and phthalimidine aromatic polyester. (See P. W. Morgan, Linear Condensation Polymers From Phenolphthalein and Related Compounds, Journal of Polymer Science: Part A, (1964) 19: 437-459). The phthalimidine copolymers are reported to rapidly discolor on UV exposure. These results suggest that the alkyl phthalimidine polycarbonates would also have poor UV stability. Contrary to these results, we have found that these copolymers have excellent UV stability (comparable to bisphenol-A based polycarbonate).
We have also found that selected phenolphthalimidine homo and copolycarbonates are useful in the same applications found useful for phenolphthalein copolycarbonates, but advantageously articles molded from them are more UV stable, have adequate melt stability and good ductility. The phenolphthalimidine based polymer resins are also free of the objectionable coloration associated with the phenolphthalein monomer, homo and copolycarbonates.
Other advantages of the resins of the invention will be described more fully below.